LETTERS

Author reply to: estimation of global visual impairment due to uncorrected refractive error

Silvio Mariotti¹; Serge Resnikoff; Donatella Pascolini

Chronic Disease Prevention and Management, World Health Organization, 20 avenue Appia, 1211 Geneva 27, Switzerland

In response to the letter by L Dandona & R Dandona,¹ we would like to point out that the study to which they refer (BMC Medicine 2006;4:6) - certainly a useful study in its own right - was not included in the references of our own paper as it informed neither the approach we took to our analysis nor the geographical scope of our work. Our study included data sources for all age groups from 68 surveys in 31 countries, chosen with epidemiological criteria diferent from those used by L Dandona & R Dandona, who derived their global estimates from nine surveys in eight countries. Our work presents an age-specifc algorithm developed for missing data.

May we also point out a misinterpretation of our fndings in this letter with regard to India. According to the estimated presenting and best-corrected blindness (visual acuity < 6/60) for people aged 50 years and older in 15 Indian states reported by Murthy et al.,² the reduction of visual impairment after correction is 42% and not one-ffth. Te authors themselves point this out by saying that "the blindness load could be nearly halved by correction".

We agree with L Dandona & R Dandona's emphasis on the need for new defnitions. Tis issue has been extensively discussed since a consultation on refractive errors held by WHO in 2000. Te International Council of Ophthalmology adopted a resolution in 2002, followed in 2003 by a WHO consultation on the development of standards for characterization of visual loss and visual functioning, which led to signifcant changes in defnitions and categorizations.³ Tese have been subsequently integrated into the revision of the 10th International Classifcation of Diseases.

References

1. Dandona L, Dandona R. Estimation of global visual impairment due to uncorrected refractive error. Bull World Health Organ 2008;86:656. doi:10.2471/BLT.08.053652        

2. Murthy GV, Gupta SK, Bachani D, Jose R, John N. Current estimates of blindness in India. Br J Ophthalmol 2005;89:257-60. PMID:15722298 doi:10.1136/bjo.2004.056937        

3. Prevention of blindness and deafness. Consultation on development of standards for characterization of vision loss and visual functioning. Geneva: WHO;2003 (WHO/ PBL/03.91).         

1 Correspondence to Silvio Mariotti (e-mail: mariottis@who.int).